Direct travel trimmer capacitor



Sept. 13, 1966 M. A. LAFER 3,273,031

DIRECT TRAVEL TRIMMER CAPACITOR Filed Oct. 21, 1963 INVENTOR.

MATTHEW A. LAFER ATTORNEY United States Patent 3 273 031 DIRECT TRAVEL TRI MMER CAPACITOR Matthew A. Lafer, 955 Columbus Drive, Teaneck, NJ. Filed Oct. 21, 1963, Ser. No. 317,454 7 Claims. (Cl. 317249) My invention relates generally to direct travel trimmer capacitors, and particularly to a trimmer capacitor of that character in which the piston is supported at longitudinally spaced points.

It is an object of my invention to provide a construction in which a trimmer capacitor bushing and a stationary pist-on support are integral.

It is a further object of my invention to provide a direct travel trimmer capacitor construction which establishes a direct, supporting-relationship between a trimmer capacitor bushing and a piston, without any intermediate attachment means.

Yet a further object of my invention is to provide a direct travel trimmer capacitor construction which is relatively simple, economical, reliable, easily miniaturized, and has a long life.

Yet a further object of my invention is to provide a direct travel construction for a trimmer capacitor which produces linear changes in capacitance, is substantially free of random movement or wob-bling of the movable electrode.

A further object of my invention is to provide a direct travel construction for a trimmer capacitor, which is capable of stable adjustments, substantially free of air gap changes with respect to the movable electrode and the bore of the dielectric mounting for the stationary electrode.

A still further object of my invention is to provide a longitudinally movable electrode which does not rotate, and maintains a relatively constant relationship to the fixed electrode.

It is a further object of my invention to provide a movable electrode or piston which is supported at two unvarying longitudinally spaced points, and is slideably positioned with respect to one support point.

Among the further objects of my invention is to provide a drive-nut as a movable support for a piston, which drive-nut is dimensioned to receive a sleeve which defines a stationary slidable support for the piston.

These objects and advantages may be attained by the device shown by way of illustration in the drawings in which:

FIGURE 1 is a perspective View with part of the sleeve, piston, support and bushing exploded.

FIGURE 2 is a perspective view of the piston.

FIGURE 3 is an inside view of the piston and the support.

FIGURE 4 is a perspective view of the adjustment screw and spring washer.

FIGURE 5 is a partial vertical sectional view of the bushing, sleeve, and support.

FIGURE 6 is a perspective view of the drive-nut.

FIGURE 7 is an end view of the support entering the drive-nut. j

A linear movement of a piston is a desirable construction to achieve linear increments of capacitance, free of reversals. In highly sensitive capacitors, or where there is a high capacitance to volume ratio, the dielectric element may be very thin, and air gap changes may cause reversals in capacitance. This type of construction frequently does not produce linear increases or decreases .in capacitance by reason of inadequate support for the piston. I have found it possible to eliminate such undesirable effects, by providing a piston which is slideably mounted on a fixed noncircular, rigid support. The piston therefore does not rotate, and is only subject to longitudinal "ice movement. In addition, the piston isalso supported at a second point, by a drive nut. With two relatively stable supports for the piston spaced at all times at a fixed distance from each other, it is possible to maintain the air gap relationship between the piston and the bore of the dielectric mounting for the stationary electrode in a precise manner, so that the air gap is not substantially varied by random movements of a rotating piston.

Referring now to the drawings in detail, the embodiment of my invention provides a conduutive bushing 11 of a generally tubular shape with an external thread 12 applied. There is radial flange 14 on the bushing 11. A cavity 15 in the bushing. is defined at one end by the shoulder 16 which is an inward extension of the radial flange 14. An adjustment screw 17 is inserted into the cavity 15. An enlargement 18 on the adjustment screw limits the longitudinal movement of the adjustment screw in one direction. The enlargement 18 is longitudinally shorter than the cavity 15, and leaves an empty portion at the outer end of the cavity 15. An axial hub 19 with an end slot 20, is formed coaxially and integrally with the enlargement 18. A spring washer 21 is engaged with the enlargement 18. The end 22 of the bushing 11 is rolled over but only sufiiciently to retain the washer 21, yet to leave aperture 23 sufficient to receive a screw driver to engage the slot 20 in the screw 17. The turned over end 22 defines a lip which will retain the spring washer 21 in the cavity 15, and normally the springwasher 21 will seat the enlargement 18 on the shoulder 16. The threaded portion of the screw 17 fits very closely in the aperture of the shoulder 16, and the enlargement likewise fits very closely in the cavity 15. Very precise axial alignment is attained.

Attached to the flange 14, near its peripheral edge is a generally tubular dielectric hollow sleeve 24. This sleeve 24 serves to mount an electrode 25 on its external surface. Inside of the sleeve 24, a conductive tubular stationary support 26 is formed integrally with the flange 14, and extends from the surface of the flange 14 in the same genera-l direction as the sleeve 24 extends, but is shorter in length than the hollow sleeve 24. The support 26 is arranged concentrically within the sleeve 24. It is of non-circular cross section as appears from FIGURE 3, for it has flattened sides 34, and is positioned concentric with the internal surface of the sleeve 24. This support 26 surrounds a portion of the adjustment screw 17.

A movable hollow piston 27 of conductive material is positioned within the sleeve 24 and is dimensioned to precisely fit inside the sleeve 24 with minimal clearance. The end of the piston 27 is formed inwardly to form an end wall 28, such end wall having a noncircular aperture 35 in general conformity to the flattened sides 34 of the support 26, and slideably mounted thereon. By reason of the flat sides 34 of the support 26 and the aperture 35 defined by the end wall 28, the piston 27 can slide longitudinally on the support 26, but cannot rotate. The piston 27 may move or slide along the support 26 until its end wall 28 is against the flange 14, at which point its capacitance-relationship with the electrode 25 will be minimal; or on the other hand, the piston 27 may move in the opposite direction longitudinally until the end wall 28 is near the end of the support 26, in which case the piston 27 has reached its maximum movement in that direction with relation to the electrode 25.

The piston 27, in addition to being supported on the support 26, is supported by the drive nut 30 which is internally attached to the piston 27 at or near the opposite open end. The exact point of attachment is not critical, as long as that point is spaced from the end wall 28 sufiiciently to provide proper support for the piston 27. If short length of the capacitor is important, greater miniaturization can be attained by attaching the drive nut 30 further inside of the piston 27; this enables the use of a shorter adjustment screw 17. The drive nut 30-has a bore which is threaded and engaged with the adjustment screw 17. A C-washer 36 on the end of the adjustment screw 17 will prevent the drive nut 30 from riding off the end of the screw 17. The drive nut 30 may be provided with a vertical slot 40 intersecting with the threaded central aperture. It may also be provided with an arcuate cut out portion 41 on top, and a bottom cut out portion 42 to receive the segments of the support 26, as hereinafter desscribed. Since the drive nut 30 is preferably made of thin material, the arms 43 adjacent to the slot 40 may be deformed inwardly to exert a clinching effort upon the drive screw 17, thereby insuring against backlash. Or, the drive nut 30 may be slightly concaved before it is applied to the piston 27, so that when the drive nut 30 recovers, it will develop an anti-backlash squeeze on the screw 17 The support 26 is provided with longitudinal slots 44 on either side. These slots define top and bottom prongs 45, 46 which enter the slots 41, 42 with complete clearance of the drive nut 30 and free of any contact with those slots. This enables the shortening of the adjustment screw 17 and for miniaturization, since the prongs 45, 46 may pass through the lots 41, 42 in the drive nut 30 Although I have shown the drive nut 30 to be attached near the end of the piston 27, it may in fact be spaced inwardly, a considerable distance from the end of the piston 27, and attached at some point to the interior portion of the piston 27.

The support provided by the drive nut 30 and the bent over portion 28 riding up on the support 26, enable precise wobble-free positioning of the piston 27 within the dielectric member 24. Since the capacitance elTect is dependent upon precise relationships existing between the electrode 25 and the piston 27, and their respective movements with relation to each other, precise predetermined linear increases or decreases in capacitance will be possible by adjustment of the screw 17 and the perpendicular distance between the electrode 25 and the piston 27 will at all times be unvarying. The construction minimizes the possibility of any Wobble or rotation of the piston 27.

Likewise, since the drive nut 30 is assembled so as to clinch the thread on the adjustment screw 17, backlash is minimized upon reversal or turning of the adjustment screw 17. By dimensioning the bushing 11 with an internal diameter which closely conforms to the external diameter of the enlargement 18, wobbling of the adjustment screw 17 is substantially eliminated. The screw 17 should be completely clear of the bore of the support 26. Thespring-washer 21 normally urges the adjustment screw 17 against the shoulder 16 and into coaxial relationship with the support 26, which is also coaxially positioned with respect to the sleeve 24 and the electrode 25. The noncircular configuration of the opening 35 defined by the end wall 28, and the flat sides 34 of the support 26, also insure stabilized capacitative relationship between the piston 27 and the electrode 25, since the piston 27 does not turn, but only moves in a longitudinal direction on two supports without turning.

Definition: Direct travel as used herein is defined as the longitudinal, movement of an element of a trimmer capacitor without rotation, as distinguished from longitudinal, rotational, movement of that element.

The foregoing description is intended to be merely illustrative of one embodiment of the invention for many changes may be made therein within the scope of the claims without departing from the spirit of the invention.

What is claimed:

1. A direct travel trimmer capacitor comprising:

(a) a stationary piston support;

(b) a generally fiat drive nut defining a movable piston support;

(c) an adjustment screw in threaded engagement with the movable piston support;

(d) a piston connected to the movable support and slidably engaged with. the stationary support;

(e) the stationary support and the piston having a noncircular configuration whereby the piston is restrained from rotation;

(f) the stationary support having a slot;

(g) the movable support having an aperture dimensioned to receive the stationary support with complete clearance;

(h) arms on the movable support dimension to pass through the slot.

2. A direct travel trimmer capacitor comprising:

(a) a stationary piston support;

(b) a generally flat drive nut defining a movable piston support;

(c) an adjustment screw in threaded engagement with the movable piston support;

(d) a piston connected to the movable support and slidably engaged with the stationary support;

(e) the stationary support and the piston having a non-circular configuration whereby the piston is restrained from rotation;

(f) the drive nut having a central, threaded aperture and a slot intersecting that aperture, with the portions of the drive nut adjacent to the intersection being deformed to exert a clinching effort upon the drive screw.

3. A direct travel trimmer capacitor comprising:

(a) a stationary piston support;

(b) a generally flat drive nut defining a movable piston support;

(c) an adjustment screw in threaded engagement with the movable piston support;

(d) a piston connected to the movable support and slidably engaged with the stationary support;

(e) the stationary support and the piston having a nonci-rcular configuration whereby the piston is restrained from rotation;

(f) the stationary support having a slot;

(g) the movable support having an aperture dimensioned to receive the stationary support with complete clearance;

(h) arms on the movable support dimensioned to pass through the slot;

(i) the drive nut having a central, threaded aperture and a slot intersecting that aperture, with the portions of the drive nut adjacent to the intersection being deformed to exert a clinching effort upon the drive screw.

4. A direct travel trimmer capacitor comprising:

(a) a stationary piston support;

(b) a generally fiat drive nut defining a movable piston support;

(0) an adjustment screw in threaded engagement with the movable piston support;

(d) a piston connected to the movable support and slidably engaged with the stationary support;

(e) the stationary support and the piston having a non-circular configuration whereby the piston is restrained frorn rotation;

(f) the generally, flat drive nut being relatively thin and extending perpendicular to the axis of the adjustment screw;

g) the drive nut having a central, threaded aperture and a slot intersecting that aperture, with the portions of the drive nut adjacent to the intersection being deformed to exert a clinching eiTort upon the drive screw.

5. A direct travel trimmer capacitor comprising:

(a) a stationary piston support;

(b) a generally flat drive nut defining a movable piston support;

(c) an adjustment screw in threaded engagement with the movable piston support;

(d) a piston connected to the movable support and slidably engaged with the stationary support;

(e) the stationary support and the piston having a noncircular configuration whereby the piston is restrained from rotation;

(f) the adjustment screw extending through the stationary support.

6. A direct travel trimmer capacitor comprising:

(a) a conductive bushing With a cavity therein to retain the head of an adjustment screw against longitudinal movement;

(b) a dielectric hollow sleeve member attached to the bushing and extending from one surface of the busha;

(c) an adjustment screw extending at one end into the dielectric hollow member and with the other end rotatably held in the cavity in the bushing;

(d) an electrode on the dielectric hollow sleeve member;

(e) a conductive hollow piston at least partly within the dielectric hollow sleeve member and coaxial therewith;

(f) a movable support engaged with the hollow piston and in threaded engagement with the adjustment screw;

(g) a stationary conductive support on the bushing within the dielectric hollow member and dimensioned to enter the piston;

stationary support;

(i) both the portion of the piston slidably mounted on the stationary support and the stationary support having a noncircular configuration whereby the piston will not rotate on the support.

7. A direct travel trimmer capacitor comprising:

(a) a stationary piston support;

(b) a movable piston support;

(c) an adjustment screw in threaded engagement with the movable piston support;

(d) a piston connected to the movable piston support and slidably engaged with the stationary support;

(e) the movable piston support having an aperture dimensioned to receive the stationary support;

(f) the piston having a nonci-rcular configuration at the point of slidable engagement with the stationary support;

(g) the adjustment screw extending through the stationary support.

References Cited by the Examiner UNITED STATES PATENTS 2,748,327 5/ 1956 Wadsworth 317249 3,051,879 9/1962 Lazar 317-249 3,071,716 1/1963 Young 317-249 3,166,695 1/1965 Barnes 3l7-249 3,206,659 9/1965 Goodman 317249 LEWIS H. MYERS, Primary Examiner. JOHN F. BURNS, ROBERT K. SCHAEFER, Examiners. E. GOLDBERG, Assistant Examiner. 

1. A DIRECT TRAVEL TRIMMER CAPACITOR COMPRISING: (A) A STATIONARY PISTON SUPPORT; (B) A GENERALLY FLAT DRIVE NUT DEFINING A MOVABLE PISTON SUPPORT; (C) AN ADJUSTMENT SCREW IN THREADED ENGAGEMENT WITH THE MOVABLE PISTON SUPPORT; (D) A PISTON CONNECTED TO THE MOVABLE SUPPORT AND SLIDABLY ENGAGED WITH THE STATIONARY SUPPORT; (E) THE STATIONARY SUPPORT AND THE PISTON HAVING A NONCIRCULAR CONFIGURATION WHEREBY THE PISTON IS RESTRAINED FROM ROTATION; (F) THE STATIONARY SUPPORT HAVING A SLOT; (G) THE MOVABLE SUPPORT HAVING AN APERTURE DIMENSIONED TO RECEIVE THE STATIONARY SUPPORT WITH COMPLETE CLEARANCE; (H) ARMS ON THE MOVABLE SUPPORT DIMENSION TO PASS THROUGH THE SLOT. 